BMB 1 - Somatosensation

Question 1

Name the four primary somatosensory modalities.

TPTPK

Answer 1

Touch-pressure

Temperature

Pain

Kinesthetic sensation

Question 2

What is 2-point discrimination?

Answer 2

The ability to detect two points as distinct stimuli on the skin

Question 3

____________ is the ability to recognize the shape or identity of familiar objects by palpation and manipulation alone.

Answer 3

Stereognosis is the ability to recognize the shape or identity of familiar objects by palpation and manipulation alone.

Question 4

____________ is the ability to recognize figures or shapes, with eyes closed, by tracing their outline on the skin with some object.

Answer 4

Graphesthesia is the ability to recognize figures or shapes, with eyes closed, by tracing their outline on the skin with some object.

Question 5

Via what tool is one’s vibration sense tested in a clinical setting?

Answer 5

A tuning fork

Question 6

Via what two mechanisms is the intensity of a stimulus coded by sensory nerves?

Answer 6

Action potential frequency (linear coding)

+

recruitment of neighboring fibers

Question 7

True/False.

Each sensory receptor has a certain adequate stimulus that must be reached in order to produce a sensation.

Answer 7

True.

Question 8

True/False.

Neurons in the CNS have spontaneous activity (i.e. they are not completely off or inhibited).

Answer 8

True.

This means sensation is often a change from baseline firing, not just the presence or absence of firing.

Question 9

Which form of quickly adapting sensory receptor is specifically tuned to vibration?

Answer 9

Pacinian corpuscles

Question 10

What term is given to the specialized free nerve endings which give rise to A-delta and C fibers?

Answer 10

Nociceptors

Question 11

________ fibers carry sensation for ‘fast,’ sharp pains and have mechanosensitive and mechanothermal nociceptors.

Answer 11

A-delta fibers carry sensation for ‘fast,’ sharp pains and have mechanosensitive and mechanothermal nociceptors.

Question 12

_______ fibers carry sensation for ‘slow,’ dull, burning pains and have polymodal nociceptors (responding to different sensations, including pain and temperature).

Answer 12

C fibers carry sensation for ‘slow,’ dull, burning pains and have polymodal nociceptors (responding to different sensations, including pain and temperature).

Question 13

The _________ field is the scope of either deep tissue or specific cutaneous surface which a single nerve innervates.

Answer 13

The receptive field is the scope of either deep tissue or specific cutaneous surface which a single nerve innervates.

Question 14

True/False.

An area of skin with a higher spatial discrimination indicates a higher density of larger receptive fields.

Answer 14

False.

An area of skin with a higher spatial discrimination indicates a higher density of smaller receptive fields.

Question 15

Within overlapping receptive fields, what process can sensory neurons use to provide a higher degree of spacial acuity that involves interactions between the neurons?

What type of configuration does this create?

Answer 15

Lateral inhibition

(suppression of surrounding neurons in order to highlight stimulus location in affected receptive field);

center-surround configuration

Question 16

What process allows for sensations to be ignored in favor of a stronger and/or more important stimulus?

(I.e. differing degrees of attention can be given to stimuli based on intensity or modality.)

Answer 16

Descending inhibition

(the cortex sends inhibitory signals back to dorsal column and thalamic areas via corticofugal pathways)

Question 17

True/False.

Descending inhibition leads to varying degrees of attention paid to different stimuli.

Lateral inhibition leads to a high degree of acuity and contrast in locating a stimulus.

Answer 17

True.

Question 18

A patient has a loss of discriminative ability, but she can still detect the stimuli.

This is a common feature of lesions to what structure(s)?

Answer 18

The somatosensory cortex

Question 19

The primary somatosensory cortex is the area that receives the most direct and most dense projections (i.e. the most detailed somatotopic organization) from the _______ and is necessary for spatial-temporal discriminations of cutaneous stimuli.

Answer 19

The primary somatosensory cortex is the area that receives the most direct and most dense projections (i.e. the most detailed somatotopic organization) from the skin and is necessary for spatial-temporal discriminations of cutaneous stimuli.

Question 20

Which is typically larger, peripheral receptive fields, or their cortical counterparts?

Answer 20

• *Peripheral receptive fields**
• (meaning there is some convergence in the cortex of peripheral stimulatory inputs)*

Question 21

What are the purposes of the medial lemniscus / dorsal column pathway?

Answer 21

Discriminative sensation (2-point, stereognosis, graphesthesia, etc.);

conscious proprioception;

pressure, vibration

Question 22

Where do the second-order neurons of the medial lemniscus pathway decussate?

Answer 22

The medial lemniscus

(projecting from the medullary nuclei gracilis and cuneatus)

Question 23

Describe the pathway of the neurons of the medial lemniscus system.

Answer 23

1st-order: Sensory receptor to ascending ipsilaterally in the spinal cord to decussate at the nucleus gracilis or cuneatus (closed medulla)

2nd-order: Nucleus gracilis or cuneatus to ventral posterolateral nucleus (thalamus)

3rd-order: Ventral posterolateral nucleus (thalamus) through the interior capsule to the primary somatosensory cortex

Question 24

Where are the two synapses of the medial lemniscus / dorsal column pathways?

Answer 24

(1) Cuneatus/gracilis nucleus (closed medulla)
(2) Ventral posterolateral nucleus (thalamus)

Question 25

True/False.

The medial lemniscus is made up of the arcuate fibers decussating and projecting contralaterally from the nuclei gracilis and cuneatus to the ventral posterolateral nucleus.

Answer 25

True.

Question 26

What are the purposes of the spinothalamic pathway?

Answer 26

Non-discriminative sensation (i.e. crude touch);

pain;

temperature

Question 27

Describe the pathway of the neurons of the spinothalamic pathway.

Answer 27

1st-order: Sensory receptor to synapse in the dorsal horn (spinal cord)

2nd-order: Dorsal horn to near-immediate decussation in the anterior white commissure and contralateral ascent to the ventral posterolateral nucleus

3rd-order: Ventral posterolateral nucleus (thalamus) through the interior capsule to the primary somatosensory cortex

Question 28

Where are the two synapses of the spinothalamic pathways?

Answer 28

(1) Dorsal horn nucleus (spinal cord)
(2) Ventral posterolateral nucleus (thalamus)

Question 29

Where do the second-order neurons of the spinothalamic tract decussate?

Answer 29

The anterior white commissure

(projecting from the dorsal horn of the spinal cord)

Question 30

Describe the pathway of the neurons carrying discriminative tactile sense from the head.

Answer 30

1st-order: Sensory receptors connected to the trigeminal ganglia synapse in the chief sensory nucleus of V (CN V nucleus in the brainstem)

2nd-order: CN V projections to the medial lemniscus travel to the ventral posteromedial nucleus (thalamus)

3rd-order: Ventral posteromedial nucleus (thalamus) to the primary somatosensory cortex

Question 31

Where are the two synapses of neurons carrying the discriminative tactile sense from the head?

Answer 31

(1) Chief sensory nucleus of V (brainstem)
(2) Ventral posteromedial nucleus (thalamus)

Question 32

Where do the second-order neurons of the neurons carrying discriminative tactile sense from the head decussate?

Answer 32

The medial lemniscus

(in this case, projecting from the chief sensory nucleus of V and then traveling to the ventral posteromedial nucleus)

Question 33

Describe the pathway of the neurons of the ventral trigeminothalamic pathway.

Answer 33

1st-order: Sensory receptor neurons with bodies in the trigeminal ganglia send axons to the mid-pons, which then descend to the spinal nucleus of V (medulla)

2nd-order: Spinal nucleus of V to decussate and ascend as the ventral trigeminothalamic pathway to the ventral posteromedial nucleus (thalamus)

3rd-order: Ventral posteromedial nucleus to the primary somatosensory cortex

Question 34

Where are the two synapses of the ventral trigeminothalamic pathway?

Answer 34

(1) Spinal nucleus of V (medulla)
(2) Ventral posteromedial nucleus (thalamus)

Question 35

What are the purposes of the ventral trigeminothalamic pathway?

Answer 35

Facial pain / temperature sensation

Question 36

Where do the second-order neurons of the pathway carrying facial pain/temperature sensation decussate?

Answer 36

The ventral trigeminothalamic pathway

(projecting from the spinal nucleus of V to the ventral posteromedial nucleus)

Question 37

Before (inferior to) the pyramidal decussation, lesions of the medial lemniscus system result in _____lateral sensory defects.

Answer 37

Before (inferior to) the pyramidal decussation, lesions of the medial lemniscus system result in ipsilateral sensory defects.

Question 38

After (superior to) the pyramidal decussation, lesions of the medial lemniscus system result in _____lateral sensory defects.

Answer 38

After (superior to) the pyramidal decussation, lesions of the medial lemniscus system result in contralateral sensory defects.

Question 39

True/False.

Lesions to the spinothalamic tract always cause contralateral deficits in pain/temperature sensation.

Answer 39

True.

Question 40

Regarding the medial lemniscus system:

In the pons, lower body somatotropy is ________ to upper body somatotropy.

In the medulla (and decussated medial lemniscus), lower body somatotropy is ________ to upper body somatotropy.

In the spinal cord, lower body somatotropy is ________ to upper body somatotropy.

Answer 40

Regarding the medial lemniscus system:

In the pons, lower body somatotropy is lateral to upper body somatotropy.

In the medulla (and decussated medial lemniscus), lower body somatotropy is ventral to upper body somatotropy.

In the spinal cord, lower body somatotropy is medial to upper body somatotropy.

Question 41

Regarding the spinothalamic tract:

In the pons, lower body somatotropy is ________ to upper body somatotropy.

In the medulla (and decussated medial lemniscus), lower body somatotropy is ________ to upper body somatotropy.

In the spinal cord, lower body somatotropy is ________ to upper body somatotropy.

Answer 41

Regarding the spinothalamic tract:

In the pons, lower body somatotropy is lateral to upper body somatotropy.

In the medulla (and decussated medial lemniscus), lower body somatotropy is lateral to upper body somatotropy.

In the spinal cord, lower body somatotropy is lateral to upper body somatotropy.